The present invention relates to compounds that are useful as catalyst activator components. More particularly the present invention relates to such compounds that are particularly adapted for use in the coordination polymerization of unsaturated compounds having improved activation efficiency and performance. Such compounds are particularly advantageous for use in a polymerization process wherein catalyst, catalyst activator, and at least one polymerizable monomer are combined under polymerization conditions to form a polymeric product.
It is previously known in the art to activate Ziegler-Natta polymerization catalysts, particularly such catalysts comprising Group 3-10 metal complexes containing delocalized .pi.-bonded ligand groups, by the use of an activator. Generally in the absence of such an activator compound, also referred to as a cocatalyst, little or no polymerization activity is observed. A class of suitable activators are aluminoxanes, or alkylaluminoxanes, which are generally believed to be oligomeric or polymeric alkylaluminoxy compounds, including cyclic oligomers. Generally such compounds contain, on average about 1.5 alkyl groups per aluminum atom, and are prepared by reaction of trialkylaluminum compounds or mixtures of compounds with water (Reddy et al, Prog. Poly. Sci., 1995, 20, 309-367). The resulting product is in fact a mixture of various substituted aluminum compounds including especially, trialklyaluminum compounds (resulting from incomplete reaction of the trialkylaluminum starting reagent or decomposition of the alumoxane). The amount of such free trialkylaluminum compound in the mixture generally varies from 1 to 50 percent by weight of the total product. Examples of alumoxanes include methylalumoxane (MAO) made by hydrolysis of trimethylaluminum as well as modified methylalumoxane (MMAO), made by hydrolysis of a mixture of trimethylaluminum and triisobutylaluminum. MMAO advantageously is more soluble in aliphatic solvents than is MAO.
A different type of activator compound is a Bronsted acid salt capable of transferring a proton to form a cationic derivative or other catalytically active derivative of such Group 3-10 metal complex. Preferred Bronsted acid salts are such compounds containing a cation/anion pair that is capable of rendering the Group 3-10 metal complex catalytically active. Suitable activators comprise fluorinated arylborate anions, most preferably, the tetrakis(pentafluorophenyl)borate anion. Additional suitable anions include sterically shielded diboron anions of the formula: ##STR1##
wherein:
S is hydrogen, alkyl, fluoroalkyl, aryl, or fluoroaryl, Ar.sup.F is fluoroaryl, and X.sup.1 is either hydrogen or halide, disclosed in U.S. Pat. No. 5,447,895.
Examples of preferred charge separated (cation/anion pair) activators are protonated ammonium, sulfonium, or phosphonium salts capable of transferring a hydrogen ion, disclosed in U.S. Pat. Nos. 5,198,401, 5,132,380, 5,470,927, and 5,153,157, as well as oxidizing salts such as carbonium, ferrocenium and silyilium salts, disclosed in U.S. Pat. Nos. 5,350,723, 5,189,192 and 5,626,087.
Further suitable activators for the above metal complexes include strong Lewis acids including (trisperfluorophenyl)borane and trs(perfluorobiphenyl)borane. The former composition has been previously disclosed for the above stated end use in EP-A-520,732, and elsewhere, whereas the latter composition is disclosed in Marks, et al., J. Am. Chem. Soc., 118, 12451-12452 (1996). Additional teachings of the foregoing activators may be found in Chen, et al, J. Am. Chem. Soc. 1997, 119, 2582-2583, Jia et al, Organometallics, 1997, 16, 842-857. and Coles et al, J. Am. Chem. Soc. 1997, 119, 8126-8126. All of the foregoing salt and Lewis acid activators in practice are based on perfluorophenyl substituted boron compounds. Although the quantity of such activator compound used is quite low, residual boron and fluorinated benzene values remaining in the polymer may be detrimental to final polymer properties, such as applications requiring high dielectrical properties.
In U.S. Pat. No. 5,453,410, an alumoxane, particularly methylalumoxane, was disclosed for use in combination with constrained geometry, Group 4 metal complexes, especially in a molar ratio of metal complex to alumoxane of from 1/1 to 1/50. This combination beneficially resulted in improved polymerization efficiency. Similarly, in U.S. Pat. Nos. 5,527,929, 5,616,664, 5,470,993, 5,556,928, 5,624,878, various combinations of metal complexes with trispentafluorophenyl boron cocatalyst, and optionally an alumoxane, were disclosed for use as catalyst compositions for olefin polymerization.
Despite the satisfactory performance of the foregoing catalyst activators under a variety of polymerization conditions, there is still a need for improved cocatalysts for use in the activation of various metal complexes under a variety of reaction conditions. In particular, it is desirable to remove boron containing contaminating compounds from such activator composition. Such boron containing contaminating compounds result primarily from ligand exchange with the alumoxane, and comprise trialkylboron compounds having from 1 to 4 carbons in each alkyl group, for example, trimethylboron, triisobutylboron, or mixed trialkylboron products. It would be desirable if there were provided compounds that could be employed in solution, slurry, gas phase or high pressure polymerizations and under homogeneous or heterogeneous process conditions having improved activation properties, that lack such trialkylboron species.
It is known that an exchange reaction between aluminum trialkyl compounds and tris(perfluorophenyl)borane occurs under certain conditions. This phenomenon has been previously described in U.S. Pat. No. 5,602,269. Tris(perfluorophenyl)aluminum is a strong Lewis acid as well. However, it generally performs poorly by itself as an activator compared with trs(perfluorophenyl)borane. Similarly, It has further been demonstrated that active catalysts resulting from the use of an aluminate anion based upon tris(perfluorophenyl)aluminum for the activation of ansa-metallocenes and biscyclopentadienyl derivatives of zirconium(IV) are generally of lower activity than those formed by the corresponding borane (Ewen, Stud. in Surf. Sci. Catal. 1994, 89, 405-410). The foregoing tri(fluoroaryl)aluminum compounds are considered to be moderately shock and temperature sensitive and difficult to handle in the pure state. In order to avoid this problem, the compounds may be prepared as adducts with Lewis bases such as ethers. Disadvantageously, however, the presence of an ether detrimentally affects the ability to use the compounds as activators for metal complexes, whereas, removing the ether can result in detonation of the compound.